class Solution(object):
    def findTheDifference(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: str
        """
        # ASCII码
        s_sum = sum((i) for i in s)
        t_sum = sum(ord(i) for i in t)
        return chr(t_sum - s_sum)


if __name__ == '__main__':
    s = Solution()
    print(s.findTheDifference('a', 'aa'))
